(19) Pelvic Viscera

THE URINARY BLADDER

The Ureters

The ureters are tubes that transport urine from the kidneys to the bladder. They enter the true pelvis near the point where the common iliac arteries branch into the external and internal iliac arteries. They follow the lateral wall of the true pelvis, positioned just deep to the peritoneum and anterior to the internal iliac arteries.

Sex-Specific Path of the Ureters

• In Women: The ureters pass inferior to the broad ligament of the uterus and enter the bladder near the fornix of the vagina.

• In Men: The ureters run just deep to the peritoneum and are crossed by the ductus deferens. At the point where they enter the bladder, they are obscured by the seminal vesicles and the ampullae of the ductus deferens.

Functional Anatomy of Ureter Entry

In both sexes, the ureters enter the bladder at an oblique angle. This specific orientation serves a vital physiological function: when the bladder fills, the expanding walls of the bladder pinch the ureters shut. This mechanical closure prevents the reflux of urine back into the ureters when the bladder is distended.

Clinical Correlation: Kidney Stones

Kidney stones, technically referred to as ureteric calculi, cause excruciating pain as they pass through the ureter. Treatment methods include:

• Disruption via ultrasound or shock waves.

• Removal through traditional surgery.

• Removal through endoscopic surgery.

Anatomy of the Bladder

In Latin, the word for bladder is vesica. Consequently, anatomical structures related to the bladder utilize the prefix "vesico-" (e.g., the vesicouterine pouch) or the suffix "-vesical" (e.g., the rectovesical pouch). The adjective describing the urinary bladder is also vesical (e.g., the superior vesical arteries).

Shape and Surfaces

The bladder is composed of an apex, a base, a superior surface, and two inferolateral surfaces. Using the metaphor of a stubby, upside-down iron:

• Apex: Corresponds to the point of the iron; it points toward the pubic symphysis.

• Superior Surface: The "hot surface" of the iron.

• Base: Where the iron sits.

• Inferolateral Surfaces: Slope toward the handle.

The shape of an empty bladder is influenced by surrounding structures: the base is flattened by either the vagina or the rectum, and the inferolateral surfaces are in contact with the levator ani muscles. When full, the bladder becomes rounded and can extend superiorly as far as the level of the umbilicus.

Internal Features and Nerve Control

• Trigone: While most of the inner surface of an empty bladder is corrugated, the trigone is a smooth, triangular patch lining the base. The ureters enter the bladder near the superior angles of the trigone, while the urethra begins at the inferior angle.

• Sensitivity: The trigone is highly sensitive to stretch and serves to signal when the bladder is distended.

• Muscle Layers: The bladder wall consists of smooth muscle. Near the neck of the bladder, these muscles form the involuntary internal sphincter of the bladder.

• Innervation: Parasympathetic nerve fibers provide motor input to the smooth muscle of the bladder and are inhibitory to the involuntary internal sphincter. When stimulated (such as by distension), they cause the bladder to contract and expel urine.

• Voluntary Control: This reflex is managed by higher brain centers via the voluntary contraction of the external urethral sphincter, which is innervated by the somatic fibers of the pudendal nerve.

THE URETHRA

The Female Urethra

In females, the urethra is a short muscular tube running near the anterior surface of the vagina. It passes through the pelvic diaphragm and terminates at the external urethral orifice located in the vestibule of the vagina (the space between the labia minora).

• Internal Urethral Sphincter: In females, this is functional rather than anatomic, composed of smooth muscle fibers from the neck of the bladder.

• External Urethral Sphincter: A distinct structure located distal to the internal sphincter region.

The Male Urethra

The male urethra is significantly longer and is divided into three distinct segments:

1. Prostatic Urethra: Surrounded by the prostate gland. Its posterior surface is marked by numerous openings for the prostatic ductules and the ejaculatory ducts.

2. Membranous Urethra: A short segment of tubing between the prostatic urethra and the bulb of the penis. It is surrounded by the sphincter urethrae muscle.

3. Spongy Urethra: Found within the bulb and the corpus spongiosum of the penis.

MALE INTERNAL GENITALIA

This group includes the ductus deferens, seminal vesicles, and ejaculatory ducts, along with the prostate.

Ductus Deferens

Formerly called the vas deferens, this is the continuation of the epididymis. It enters the abdomen via the spermatic cord and the true pelvis along the lateral walls, deep to the peritoneum. At the base of the bladder, it enlarges into the ampulla. The ampulla fuses with the duct of the seminal vesicle to form the ejaculatory duct.

• Vasectomy: A surgical procedure for sterilization involving the ligation and removal of a section of the ductus deferens.

Seminal Vesicles and Ejaculatory Ducts

These glands are situated between the bladder and the rectum. Despite their name, they do not store semen. They are the primary source of seminal fluid, producing:

• Fructose: The primary energy source for sperm.

• Prostaglandins: Stimulate muscle contractions in the uterus and uterine tubes to assist in moving the ovum.

At their inferior ends, they empty into a short duct that fuses with the ampulla of the ductus deferens to create the ejaculatory ducts, which then empty into the prostatic urethra.

The Prostate

In young men, the prostate is a walnut-sized gland located between the bladder and the bulb of the penis, surrounding the prostatic urethra. It generates approximately $20\%$ of seminal fluid, which enters the urethra through $20-30$ ducts in the posterior wall.

Prostatic Secretions

• Alkaline: To counteract the acidic environment of the vagina.

• Zinc: Stabilizes sperm chromatin.

• Prostate-specific antigen (PSA): Prevents the fluid from coagulating.

Clinical and Physical Considerations

The base of the prostate contacts the bladder, while the posterior surface contacts the rectum, allowing for palpation during a rectal examination. As men age, the prostate typically enlarges.

• Benign Prostatic Hypertrophy (BPH): Can obstruct urine flow, leading to nocturia (the need to void at night) and dysuria (pain during urination). This occurs in $80\%$ of men over $80$ years old.

• Prostatic Carcinoma: Common in older men, occurring in $30\%$ of men over $75$ years old.

FEMALE INTERNAL GENITALIA

This includes the vagina, uterus, uterine tubes, and ovaries.

Vagina

A muscular tube extending from the vaginal vestibule to the cervix of the uterus. It is posterior to the bladder and anterior to the rectum.

• Fornix: The recess formed around the cervix. The posterior wall of the fornix is thin and partially formed by peritoneum; damage here can lead to peritonitis.

• Sphincters: Muscles acting as vaginal sphincters include the levator ani, the sphincter urethra, and the bulbospongiosus.

Uterus

Usually flexed anteriorly over the superior wall of the bladder at a right angle to the vagina.

Parts of the Uterus

• Body: The main part.

• Cervix: The narrow inferior portion.

• Isthmus: The region where the body meets the cervix.

• Fundus: The superior part of the body between the tube entrances.

Surfaces and Pouches

• Peritoneum: The broad ligament (peritoneal folds) suspends the body.

• Vesicouterine Pouch: A peritoneal pocket between the uterus and the bladder.

• Rectouterine Pouch: A peritoneal pocket between the uterus and the rectum, extending inferiorly to the posterior wall of the vaginal fornix.

• Clinical Note: Blood (e.g., from a ruptured ectopic pregnancy) can pool in these pouches and be palpated during a vaginal exam.

Uterine Wall and Blood Supply

1. Perimetrium: Peritoneum and pelvic visceral fascia.

2. Myometrium: Smooth muscle.

3. Endometrium: Mucous coat sloughed during menstruation.

Blood is supplied by the uterine arteries (branches of the internal iliac) and the ovarian arteries (branches of the aorta).

Ovaries

Almond-shaped organs near the lateral walls of the true pelvis, located within the peritoneal cavity.

• Attachments: The mesovarium attaches the anterior surface to the broad ligament. The suspensory ligament of the ovary (containing vessels and nerves) anchors it to the lateral pelvic wall. The ligament of the ovary anchors it to the uterus. A specialized fimbrium anchors it to the infundibulum.

• Menopause: Ovaries usually atrophy after menopause.

Uterine Tubes (Fallopian Tubes)

Components of the tube from the uterus outward:

1. Uterine Part: Surrounded by myometrium.

2. Isthmus: Short, thick-walled portion near the uterus.

3. Ampulla: The longest part and the typical site of fertilization.

4. Infundibulum: Funnel-shaped distal portion opening to the peritoneal cavity, featuring finger-like fimbriae to sweep up oocytes.

Clinical Correlation

The direct connection between the peritoneal cavity and the outside world means vaginal infections can spread to cause peritonitis. If a zygote implants in the tube rather than the uterus, an ectopic tubal pregnancy occurs, which can be lethal if the tube ruptures.

UTERINE LIGAMENTS

Subdivisions of the Broad Ligament

• Mesosalpinx: Between the ovary and the uterine tube.

• Mesovarium: Anchors the ovary to the broad ligament.

• Mesometrium: Between the ovaries and the uterus.

Cord-like Ligaments

• Ligamentum Teres (Round Ligament): Originates near the fundus, passes laterally, and exits the abdominal cavity through the deep ring of the inguinal canal.

• Ovarian Ligament: Short; originates near the fundus and attaches to the uterine surface of the ovary.

• Suspensory Ligament of the Ovary: Attaches the lateral surface of the ovary to the pelvic wall and carries ovarian vessels.

Note: The ligamentum teres and ovarian ligament are remnants of the gubernaculum, the embryonic cord that pulls the ovaries from the posterior abdominal wall into the pelvis.

BLOOD SUPPLY OF THE PELVIS

The common iliac artery divides into the external iliac (supplying the lower limb) and the internal iliac (supplying pelvic viscera, perineum, medial thigh, and gluteal region).

Branches of the Internal Iliac Artery

Anterior (Visceral) Division

Most constant vessels (often in this order):

1. Umbilical Artery: Branches include superior vesical arteries. Distally becomes the medial umbilical ligament.

2. Obturator Artery: To the medial thigh.

3. Inferior Vesical Artery: Only in males.

4. Vaginal Artery: Only in females.

5. Uterine Artery: Sometimes a branch of the umbilical artery.

6. Middle Rectal Artery

7. Internal Pudendal Artery: To the perineum.

8. Inferior Gluteal Artery: To the buttocks (occasionally a branch of the posterior division).

Posterior (Parietal) Division

• Superior Gluteal Artery: Major branch to the buttocks.

Surgical Warning: The ureter is at significant risk of damage when blood vessels are clamped during a hysterectomy or ovariectomy.